SAN FRANCISCO--Red Hat and Novell, the two top Linux sellers, have only just begun building Xen virtualization software into their products. But they're already planning to add a higher-level option.

Xen is a "hypervisor" that lets a single computer run several operating systems simultaneously, using an idea called "virtualization." This enables companies to use a single server more efficiently--something that could save them money. Now "containers," a higher-level virtualization approach that makes a single operating system look like many, is also getting traction.

"I think the big advantage of a containers approach, compared to a hypervisor, is a lot less overhead. You get much higher performance," Gabriel Consulting Group analyst Dan Olds said.

Containers are increasingly popular. Sun Microsystems introduced its own container technology in 2005 with Solaris 10. And Microsoft is working on an adaptation of existing technology.

They are not suited to all tasks. Containers require all applications to use the same copy of the underlying operating system, for example. Xen and the established virtualization leader, EMC's VMware, don't have that requirement. Nevertheless, containers are desirable.

Next on the agenda
"It's something that we want to see happen," Red Hat's chief technology officer, Brian Stevens, said in an interview here during the LinuxWorld Conference & Expo. Red Hat hasn't decided whether to use OpenVZ or Vserver, he added.

Xen is the priority for RHEL 5, due to arrive at the end of the year, but after that will come containers, Stevens said. "I'm looking at that as a RHEL 6 thing," he said.

Novell, which wants to maintain Suse's reputation as the first place to find advanced new features for Linux, is more eager and is considering adding OpenVZ in Service Pack 1 of SLES 10. "We are still evaluating if this is something we can take into SP1," said Holger Dyroff, vice president of Linux product management.

If containers don't arrive with SLES 10 Service Pack 1, Novell will urge SWsoft to work with Linux programmers so that the software can be easily added to SLES 11, Dyroff said.

Debian Linux, a noncommercial version of the open-source operating system, added OpenVZ to its "Sid" development version in August.

And some work being done for Xen will help pave the way for containers. Specifically, this will provide management tools that let customers start, stop and otherwise control virtual machines. The same technology can be used to control containers, Stevens said.

"It'll be a lot easier next time. We'll be able to just plug it in. There already will be tools to manage it," Stevens said.

But SWsoft, the company that is sponsoring the OpenVZ and that sells a fuller-featured commercial version called Virtuozzo, sees things the other way around. Last week, the company announced that its container management tools will also be able to manage Xen virtual machines, said Chief Executive Serguei Beloussov.

On a diet
The main reason to use containers is because they require fewer computing resources than full-fledged virtual machines.

For example, the many components of an operating system and its applications must be loaded into memory only once, and multiple containers can use the same copy. However, containers still need unique memory for their own data storage.

Another advantage is that some processor resources are used more efficiently with containers, said Don Becker, Penguin Computing's CTO and a Linux supercomputing expert. For example, a chip's translation lookaside buffer (TLB), which converts an operating system's memory addresses into the physical locations that the computer actually uses to fetch needed information, is dramatically more useful with containers, he said.

Sun's containers, also called "zones," take only an extra 60MB of memory apiece, said John Clingan, a Sun engineer who has seen just how many he can squeeze onto a single server.

Flip side
XenSource CTO Simon Crosby agreed that containers are useful but that they're not a miracle cure.

"The container-style virtualization is fabulous when you don't need a different operating-system image for each application," he said. That circumstance is common, for example, at Web site-hosting companies where SWsoft's Virtuozzo--a big brother to OpenVZ--is popular.

"Where it falls short is where IT has legacy applications or a diversity of operating systems, and each one of those needs its own wrapper--its particular version of the operating system and drivers," Crosby said.

About the author

Stephen Shankland has been a reporter at CNET since 1998 and covers browsers, Web development, digital photography and new technology. In the past he has been CNET's beat reporter for Google, Yahoo, Linux, open-source software, servers and supercomputers. He has a soft spot in his heart for standards groups and I/O interfaces.
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